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Apple Scab and Fire Blight

News Article

by Mark Gleason, Department of Plant Pathology

These are the most serious disease problems on apple and crabapple statewide. Apple growers should have begun their fungicide spray schedule for scab control by the 1/4-inch green stage. On crabapple, scab control on highly scab-susceptible cultivars should begin at the pink or early bloom stage (this week in central Iowa), with sprays repeated twice more thereafter at intervals of 10-14 days.

This spring, we are conducting a cooperative trial on fire blight control with eight commercial apple growers in central and western Iowa. The growers are timing their streptomycin sprays for fire blight according to the risk level created by moisture and temperature conditions. The "brains" of this Integrated Pest Management technique is MARYBLYT, a computer program devised by Dr. Paul Steiner, University of Maryland, and tested extensively in the East and Midwest.

Cooperating growers are calling ISU daily via a toll-free phone line to relay their weather information, MARYBLYT is run on a personal computer, and growers are called when a strep spray is recommended. Cool conditions during April kept the risk of fire blight low, but the onset of warm weather, along with predicted showers, led MARYBLYT to recommend a streptomycin spray for several growers in western Iowa late last week. The potential risk of fire blight will peak as we move into the bloom period over much of the state during the next week. MARYBLYT should help growers in two ways: by improving the effectiveness of strep sprays, and by reducing the overall number of strep sprays they need to apply. MARYBLYT is being sold commercially this year; it costs $150, will run on any IBM or IBM-compatible with 640 kb of RAM and 170 kb of disk space, but can also be run from a floppy disk rahter than a hard drive. It's available in either 5.25" or 3.5" disk format. To order MARYBLYT, call or write: Office of Technology Liaison, University of Maryland at College Park, 4312 Knox Rd., College Park, MD 20742 (phone: 301-405-4210)